GOP (Group of Pictures) Structure
Definition
The pattern of I-frames, P-frames, and B-frames in a compressed video stream. Different cameras use different GOP lengths and frame-type ratios, which are firmware-determined and consistent across recordings from the same device.
- Frame pattern
- I, P, B frame sequence per GOP
- Determinant
- Camera or encoder firmware
- Consistency
- Stable across recordings from the same device
- Forensic use
- Source camera matching
Common questions
How does GOP structure help match a video clip to a specific camera model?+
Because the GOP length and the ratio of I, P and B frames are fixed by a device's encoder firmware, a clip showing a consistent, distinctive GOP pattern can be compared against known patterns from candidate camera models or the suspect device to support or exclude it as the source.
Can GOP structure alone confirm a specific individual camera, not just a model?+
Not usually, GOP structure is generally a firmware-level, model-wide characteristic, so it narrows the source to a class of devices sharing that firmware; other artefacts such as sensor noise pattern are needed to individualise to one physical camera.
What can disrupt GOP-based source matching?+
Re-encoding or transcoding a video, for example after upload to a social media platform, replaces the original GOP structure with the platform's own encoder settings, erasing the original camera's signature and complicating source matching.
Related terms
- Bitrate Profile
- The pattern of bitrate variation across time in a variable-bitrate recording. A camera's rate-control algorithm allocates more bits to complex scenes and...
- Codec Fingerprint
- The characteristic pattern of encoding decisions made by a camera's firmware when compressing video: the specific H.264 or H.265 profile and level,...
- Colour Pipeline
- The sequence of transformations applied to raw sensor data to produce the encoded video signal, including white balance, gamma curve, colour space...
- PRNU (Photo Response Non-Uniformity)
- The unique pattern of pixel-level sensitivity variations in a camera sensor, used as a device fingerprint. A genuine camera-original image carries the...
- Reference Profile
- A database of known parameter values built from recordings made with the suspect device under controlled conditions. Comparison of the questioned video...